Sound detection by Atlantic cod: An overview

Continuous sound from a marine vibrator causes behavioural responses of free-ranging, spawning Atlantic cod (Gadus morhua)

Marine vibrators are a new technology being developed for seismic surveys. These devices can transmit continuous instead of impulsive sound and operate over a narrower frequency band and at lower peak pressure than airguns, which is assumed to reduce their environmental impacts. We exposed spawning Atlantic cod (Gadus morhua) to sound produced by a prototype, but full-scale, marine vibrator, and monitored behavioural responses of tagged cod using acoustic telemetry. Fish were exposed to 10 × 3 h continuous sound treatments over a 4-day period using a randomised-block design. Sound exposure levels were comparable to airgun exposure experiments conducted previously with the same set-up ranging from ∼115 to 145 dB re 1 μPa2s during exposure. Telemetry data were used to assess 1) whether marine vibrator exposure displaced cod from the spawning ground, through estimation of residence and survival probabilities, and 2) fine-scale behavioural responses within the test site, namely swimming depth, activity levels, displacement, and home ranges. Forty-two spawning cod were tagged prior to the exposure, with 22 present during the exposure. All 22 tags were equipped with pressure sensors and ten of these additionally with accelerometers. While no premature departure from the spawning site was observed, cod reacted to the exposure by decreasing their activity levels (by up to 50%, SE = 7%) and increasing their swimming depth (by up to 2.5 m, SE = 1.0 m) within the test site during the exposure period. These behavioural responses varied by sex and time of day. Cod reactions to a marine vibrator may be more pronounced than reactions to airguns, possibly because continuous sound is more disturbing to fish than intermittent sound at the same exposure levels. However, given sample size limitations of the present study, further studies with continuous sound are necessary to fully understand its impact and biological significance.

Comparison of the saccules and lagenae in six macrourid fishes from different deep-sea habitatsa)

There are substantial interspecific differences in the morphology of the ears of the more than 34 000 living fish species. However, almost nothing is known about the functional significance of these differences. One reason is that most comparative studies have been conducted on shallow-water species with far less focus on the numerous species that inhabit the depths of the oceans. Thus, to get a better sense of ear diversity in fishes and its potential role in hearing, this study focuses on the saccule and lagena, the primary auditory end organs, in six species of the family Macrouridae (rattails), a large group of fishes that typically inhabit depths from 1000 to 4000 m. The inner ears and, particularly, the saccules and lagenae in these species are large with the saccule resembling that of other Gadiformes. The lagenae of all macrourids studied here have serrated edge otoliths and highly diverse hair cell ciliary bundle shapes. The differences found in the inner ear anatomy of macrourids likely reflect the sensory advantages in different habitats that are related to the benefits and constraints at different depths, the fish's particular lifestyle, and the trade-off among different sensory systems.

Atlantic cod (Gadus morhua) larvae are attracted by low-frequency noise simulating that of operating offshore wind farms

The number and size of offshore wind (OW) turbines is increasing rapidly. OW turbines produce continuous, low-frequency noise that could impact marine fish dispersing/migrating through the facilities. Any such impact would be relevant for larval stages, which have limited possibility to swim away from OW facilities. If directional movement of fish larvae at sea is impacted by low-frequency continuous sound is unknown. We observe the behavior of Atlantic cod larvae (N = 89) in response to low-frequency sound while they are drifting in a Norwegian fjord inside transparent drifting chambers. We transmit 100 Hz continuous sound in the fjord, in the intensity range of OW turbines' operational noise, and measure the sound pressure and 3-D particle motion. Half of the larvae (N = 45) are exposed to low-frequency (100 Hz) continuous sound, while the other half (N = 44) are observed under the same conditions but without the sound. Exposure does not affect the routine and maximum swimming speeds or the turning behavior of the larvae. Control larvae orient to the northwest. In contrast, exposed larvae orient towards the source of low-frequency sound and particle motion. This provides a basis to assess how OW might impact dispersal in this species.

The Sound World of Zebrafish: A Critical Review of Hearing Assessment

Zebrafish, like all fish species, use sound to learn about their environment. Thus, human-generated (anthropogenic) sound added to the environment has the potential to disrupt the detection of biologically relevant sounds, alter behavior, impact fitness, and produce stress and other effects that can alter the well-being of animals. This review considers the bioacoustics of zebrafish in the laboratory with two goals. First, we discuss zebrafish hearing and the problems and issues that must be considered in any studies to get a clear understanding of hearing capabilities. Second, we focus on the potential effects of sounds in the tank environment and its impact on zebrafish physiology and health. To do this, we discuss underwater acoustics and the very specialized acoustics of fish tanks, in which zebrafish live and are studied. We consider what is known about zebrafish hearing and what is known about the potential impacts of tank acoustics on zebrafish and their well-being. We conclude with suggestions regarding the major gaps in what is known about zebrafish hearing as well as questions that must be explored to better understand how well zebrafish tolerate and deal with the acoustic world they live in within laboratories.

Fish hearing "specialization" - A re-valuation

Investigators working with fish bioacoustics used to refer to fishes that have a narrow hearing bandwidth and poor sensitivity as "hearing generalists" (or "non-specialists"), while fishes that could detect a wider hearing bandwidth and had greater sensitivity were referred to as specialists. However, as more was learned about fish hearing mechanism and capacities, these terms became hard to apply since it was clear there were gradations in hearing capabilities. Popper and Fay, in a paper in Hearing Research in 2011, proposed that these terms be dropped because of the gradation. While this was widely accepted by investigators, it is now apparent that the lack of relatively concise terminology for fish hearing capabilities makes it hard to discuss fish hearing. Thus, in this paper we resurrect the terms specialist and non-specialist but use them with modifiers to express the specific structure of function that is considered a specialization. Moreover, this resurrection recognizes that hearing specializations in fishes may not only be related to increased bandwidth and/or sensitivity, but to other, perhaps more important, aspects of hearing such as sound source localization, discrimination between sounds, and detection of sounds in the presence of masking signals.